The present invention relates to silicon carbide coated abrasive grains, such as diamond and cubic boron nitride, and more particularly to unique randomly-oriented polycrystalline silicon carbide coatings therefor.
Taylor (U.S. Pat. No. 3,520,667) proposes to coat diamond abrasive particles with an adherent surface coating of silicon carbide by suspending the diamond particles in a gaseous atmosphere of a volatile silicon compound which is thermally decomposed to form a silicon carbide coating on the diamond particles by reaction with the carbon present in the volatile silicon compound or added gaseus source of carbon. Kuratomi (U.S. Pat. No. 3,617,347) uses an analogous vapor deposition technique to coat diamond powder with a thin film of silicon carbide formed from the gaseous silicon compound and the diamond particle itself which thin silicon carbide coating then is recoated with elemental silicon. Silicon-based alloy coatings for abrasive grains have been proposed by Otopkov (U.S. Pat. No. 4,184,853) wherein the coating is a three-component system which includes silicon and two other metals selected from a recited group of metals, and by Caveney (U.S. Pat. No. 3,929,432) wherein a titanium alloy coats the diamond grain. U.S. Pat. No. 4,174,971 describes the in situ formation of silicon carbide by a pyrolysis process.
A prime use of these various coated abrasive particles is in the formation of grinding elements wherein the coated abrasive particles are bonded together with resin, metal, vitreous material, or the like. A prevalent problem in using such bonded coated abrasive particles is that the particles tend to pull out from the bonding matrix, thus resulting in decreased grinding performance and a loss of valuable abrasive particles. The coatings on the abrasive particles provide a degree of increased retention of the particles within the bonding matrix. Still, improvements in this art are needed.